Allow GPHContent APIs with GiphyViewController

[simoalx]

Use case description

We want to have more customisation of the GiphyViewController, like we would have making the more low level GiphyGridController, e.g.

gridController.content = GPHContent.search(withQuery: "Sup", mediaType: .text, language: .english)
gridController.update()

Proposed solution

Add an API for GPHContent usage for GiphyViewController, or allow access to the underlying GiphyGridController for that vc (if it is implemented this way)

Alternatives considered

We could roll our own VC with all the more lower level components, but we'd lose the convenience of GiphyViewController.